Lymph vessels together with blood vessels run throughout tissues and organs in a body, and are responsible for protection against pathogens, immunity, elimination of waste products, and return of fluid and protein to veins. Lymph flowing through the lymph vessels is pushed out by intrinsic (autonomous) contractility (pumping ability) of the lymph vessels in collecting lymph vessels, and flows through distal portions of extremities to a body trunk, then through a thoracic duct into veins.
However, techniques for measuring pumping ability by intrinsic (autonomous) contractility of lymph vessels have not been established. This is because lymph vessels form an open circuit system unlike blood vessels' closed circuit, direct injection of a contrast dye into lymph vessels is difficult unlike angiography, and thus it is difficult to capture lymph vessels on images. A lymph flow is not a pulsatile flow like an artery, and there is no acoustic detection technique of a lymph flow. Thus, unlike blood pressure measurement, a method for measuring pressure of lymph (lymphatic pressure) flowing through lymph vessels has not been put to practical use. Like blood pressure, lymphatic pressure may be affected by aging or diseases, but this has been hardly clarified because of the technical difficulty mentioned above.
As a method for detecting a lymph flow, a lymphoscintigraphy has been performed as a clinical examination, in which a gamma camera performs scintillation counting of gamma radiation emitted by radio isotopes (RI) injected into skin or subcutaneous tissue and images the gamma radiation. Non-patent Literature 1 mentioned below describes a method for measuring lymphatic pressure of a subject using the lymphoscintigraphy. Specifically, first, a manchette (pressure cuff) is wrapped around an extremity of a subject lying on an examining table of a gamma camera, and the extremity is compressed with certain pressure to stop movement of radio isotopes in lymph vessels. Then, the pressure of the manchette is gradually reduced, and pressure at that time when the isotopes are detected beyond an area around which the manchette is wrapped is measured as lymphatic pressure.